The overall goal of this project is the assessment of sex differences in brains, including sex differences in sex hormone uptake in selected regions, and quail sex differences in the sizes of brain nuclei or regions. Determination of areas of steroid uptake and sex differences in uptake will be done by the technique of steroid autoradiography. Quail whose gonads have recently been removed will be injected with tritiated (radioactively labelled) estradiol, testosterone, or dihydrotestosterone, and brains will be removed 90 min later, sectioned onto emulsion-coated slides, and stored for 3 or more months. Slides will then be developed. Sections will be stained, and the number (percentage) of labelled cells (cell nuclei) in different areas of the brain determined. Sex differences in the sizes of regions will be determined by cutting frozen sections from brains of perfused intact adult quail, staining with cresyl violet, projecting sections at 30-100 X, and measuring perimeters to compute total volume. Future work will include: effect of steroid manipulations in adulthood or embryonic life on adult sex differences; effect on photoperiod, independent of hormone exposure, on these brain characteristics; measurement of these sex differences at different stages of development; effect of steroid implants into the brains of animals in order to determine the behavioral significance of dimorphic regions; and lesion studies of these same regions. This work will be of interest to neurobiologists, endocrinologists and developmental biopsychologists, and will contribute to our understanding of sex differences in behavior, neuroendocrine mechanisms of normal and abnormal behavior, and the effects, both normal and pathological, of hormones on the developing brain.